host: relations-as-posts slice 2 — relation metadata lives on relation-posts

is-a/subtype-of/tagged/related are now POSTS (each is-a a new `relation` root),
owning their metadata in a :rel slot {:symmetric :label :inverse-label}. The static
host/blog-rel-kinds registry is gone: kind-spec/rel-kinds/kind-symmetric? read the
relation-posts (via an in-memory cache), and the relation list derives from
host/blog-in "relation" "is-a".

Perform-budget fixes (a durable read inside the http-listen render VM raises
VmSuspended; too many per request 500s the page):
 - relation metadata is loaded into a cache at boot (host/blog-load-rel-kinds!,
   like load-edges!), so kind-spec is pure on render paths;
 - the initial edit page renders its pickers EMPTY (the load trigger fills each) —
   only the relate/unrelate FRAGMENT server-renders candidates (with-cands flag).
   Previously every edit page render did candidate-get × 4 pickers and 500'd.

host conformance 287/287 (+4 slice-2: kind-spec reads :rel, kind-symmetric? off the
post, unknown kind has no spec, rel-kinds derived from the graph). run-picker-check
3/3 (edit page boots, relate/unrelate flow works, no client errors).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

plans/relations-as-posts.md

@@ -40,11 +40,22 @@ the relation's object-end declaration from the anchor**, which includes the root
   `host/blog--candidate-pool` to be declaration-driven. `:candidates` becomes vestigial.
 - Wrinkle fixed: the type roots now appear as `is-a` candidates.
 
-### Slice 2 — relations as first-class posts
-- Seed `is-a`/`subtype-of`/`tagged`/`related` as posts that own their metadata
-  (`:symmetric`, `:label`, `:inverse-label`, **cardinality**, **end roles**). The registry
-  `host/blog-rel-kinds` melts into reads off these posts. A relation can declare its
-  *subject*-end anchor too (who may be the source), not just object.
+### Slice 2 — relations as first-class posts — DONE
+- `relation` root + `is-a`/`subtype-of`/`tagged`/`related` seeded as posts (each is-a
+  relation) owning their metadata in a `:rel` slot (`:symmetric :label :inverse-label`).
+  `host/blog-rel-kinds` / `kind-spec` / `kind-symmetric?` now read it; the static registry
+  is gone. `host/blog--rel-slugs` = `host/blog-in "relation" "is-a"` (cheap, flat).
+- **Perform budget under http-listen (the hard lesson):** a durable read inside the
+  render VM raises `VmSuspended`, and too many per request 500s the page. Two fixes:
+  (1) relation metadata is loaded into an in-memory cache at boot (`host/blog-load-rel-kinds!`,
+  like `load-edges!`) so `kind-spec` is pure; (2) the initial edit page renders its pickers
+  EMPTY (the load trigger fills each) — only the relate/unrelate FRAGMENT server-renders
+  candidates (`with-cands` flag), so one page render doesn't do `candidate-get × every
+  picker`. Benign single-perform suspend/resume still logs `VmSuspended` but returns 200.
+- **Follow-up (Slice 2.5):** `relate-candidates` does a `host/blog-get` per pool member
+  (O(posts) for `related`). A boot-time **title cache** (updated on put!/delete!) would make
+  the picker O(1)-perform and cut the suspend/resume churn. Subject-end declarations + a
+  proper relation-subtype closure (when relations get subtyped) also belong here.
 
 ### Slice 3 — typed relations (target-type constraints)
 - A declaration carries a **target-type constraint**: the *other* end must be (an instance